Conventionally, a decoloring apparatus which can decolor an image formed of decolorable coloring agent is known. Since a sheet in which a color of an image has been decolored by the decoloring apparatus is reusable, the consumption of sheets can be suppressed. The decoloring apparatus is mainly used in an office and so on. In order to effectively use the space of an office, miniaturization of the decoloring apparatus has been tried.
A decoloring apparatus has a sheet feeding unit, an image reading unit, a decoloring unit and a sheet discharge tray for reuse. Further, the decoloring apparatus has a first sheet conveying path from the sheet feeding unit toward the sheet discharge tray via the image reading unit, and a second sheet conveying path which branches from the first sheet conveying path at a branch point located at the downstream of the image reading unit and goes toward the decoloring unit. A sheet to be fed by the sheet feeding unit is conveyed to the image reading unit via the first sheet conveying path. The image reading unit reads an image formed on the sheet. The decoloring apparatus determines whether or not an image has been formed on the sheet, based on the reading result by the image reading unit. When it is determined that an image has not been formed on the sheet, the sheet is conveyed to the sheet discharge tray via the first sheet conveying path. On the other hand, when it is determined that an image has been formed on the sheet, the sheet is conveyed to the decoloring unit via the second sheet conveying path.
However, in a miniaturized decoloring apparatus, there may be a case in which a length of the sheet is longer than a distance from the image reading unit to the branch point, depending on a sheet to be dealt with. When the length of the sheet is longer, a leading edge of the sheet in the sheet conveying direction reaches the branch point, before the reading of an image of the whole of the sheet to be conveyed is finished. As described above, when it is determined that an image has been formed on the sheet, it is necessary that the sheet which has reached the branch point is conveyed to the decoloring unit via the second sheet conveying path, so as to perform the decoloring processing.
However, when an image formed on a sheet contains a confidential content, for example, the confidential content is decolored by the decoloring unit. Here, the decoloring unit heats the decolorable coloring agent at not less than a prescribed temperature, to make the color of the coloring agent colorless and transparent. But even if the coloring agent has been colorless and transparent, the coloring agent remains on the sheet while being fixed to the sheet. In other words, an image containing the confidential content comes to be formed of the coloring agent which has become transparent, on the sheet after the decoloring by the decoloring unit. The image formed of the coloring agent which has become transparent can be viewed, depending on the reflective condition of light.
Even if the image containing the confidential content has been formed on the sheet discharged after the decoloring processing, as described above, there is a possibility that a user cannot recognize the confidential content. Accordingly, the sheet formed with the image containing the confidential content is handed over to a third party, and thereby the confidential information is likely to leak to the third party. Accordingly, regarding a sheet formed with an image containing a confidential content, it is more ideal not to perform the decoloring processing to such a sheet.
However, when a length of a sheet is longer than the distance from the image reading unit to the branch point, as described above, the sheet formed with an image containing a confidential content might be conveyed to the decoloring unit. Accordingly, when the decoloring processing is performed to the sheet formed with an image containing a confidential content, the confidential information is likely to leak to a third party.